It was known to use laser-based and/or imager-based readers or scanners in a dual window or bi-optical workstation to electro-optically read targets or indicia, such as bar code symbols, associated with three-dimensional products to be identified and processed, e.g., purchased, at a point-of-transaction workstation provided at a countertop of a checkout stand in supermarkets, warehouse clubs, department stores, and other kinds of retailers. The products were typically slid or moved by a user across, or presented to and momentarily held steady at a central region of, a generally horizontal window that faced upwardly above the countertop and/or a generally vertical or upright window that rose above the countertop. When at least one laser scan line generated by a laser-based reader swept over a symbol and/or when return light from a symbol was captured over a field of view by a solid-state imager of an imager-based reader, the symbol was then processed, decoded and read, thereby identifying the product.
The symbol could be located low or high, or right to left, on the product, or anywhere in between, on any of six sides of the product. The symbol could be oriented in a picket fence orientation in which elongated parallel bars of a one-dimensional Universal Product Code (UPC) symbol were vertical, or in a ladder orientation in which the UPC symbol bars were horizontal, or at any orientation angle in between. The products could be held by the user at various tilt angles during their movement across, or presentation to, either window. The products could be moved relative to the windows in various directions, for example, from right-to-left, or left-to-right, and/or in-and-out, or out-and-in, and/or high-to-low, or low-to-high, or any combination of such directions, or could be positioned either in contact with, or held at a working distance away from, either window during such movement or presentation. All these factors made the symbol location variable and difficult to predict in advance.
As advantageous as workstations with laser-based readers were in processing transactions, workstations with imager-based readers, also known as imagers or cameras, were thought to offer improved reliability and had the added capability of reading indicia other than UPC symbols, such as two-dimensional or stacked or truncated symbols, as well as the capability of imaging non-symbol targets, such as receipts, driver's licenses, signatures, etc. Early all imager-based workstations required about ten to twelve, or at least six, imagers having multiple, intersecting fields of view extending through the windows in order to provide a full coverage scan zone in front of the windows to enable reliable reading of indicia that could be positioned anywhere on all six sides of a three-dimensional product. To bring the cost of the imager-based workstation down to an acceptable level, it was known to reduce the need for the aforementioned six to twelve imagers down to two imagers, or even one imager, by splitting the field of view of at least one of the imagers into a plurality of subfields of view, each additional subfield serving to replace an additional imager. These subfields also intersected each other in order to again provide a full coverage scan zone that extended above the horizontal window and in front of the upright window as close as possible to the countertop, and sufficiently high above the countertop, and as wide as possible across the width of the countertop. The scan zone projected into space away from the windows and grew in volume rapidly in order to cover indicia on products that were positioned not only on the windows, but also at working distances therefrom.
Each imager included an array of image sensors, and typically had an associated illuminator or illumination assembly to illuminate the indicia with illumination light over an illumination field. The image sensors detected the return illumination light reflected and/or scattered from the indicia. Each imager preferably operated at a frame rate of multiple frames per second, e.g., sixty frames per second, each frame lasting about 16.67 milliseconds. Each field of view, or each subfield, was preferably individually illuminated, and overlapped, by a respective illumination field and extended through at least one window over regions of the product. Each imager included either a global or a rolling shutter to help prevent image blur, especially when the indicia passed through the scan zone at high speed, e.g., on the order of 100 inches per second. Preferably, to reduce power consumption, to prolong operational lifetime, and to reduce bright light annoyance to operators and customers, the illumination light was not emitted at all times, but was emitted only when a proximity sensor detected the presence of a product entering the workstation. Upon product detection, the proximity sensor caused the illumination assembly to be activated.
The various multiple intersecting fields of view, or subfields, extended through a respective window along different directions, were typically differently sized to optimally cover the scan zone, and were typically simultaneously illuminated to reduce system complexity. As a result, some of the illuminated fields or subfields overlapped to different extents depending on the working distance away from a respective window. Thus, there was a substantial overlap between some of the illuminated fields or subfields at, or in a near field close to, the respective window, and less of an overlap in a far field remote from the respective window. Put another way, the illumination field in one or more fields or subfields was not uniform. There were bright areas, as a result of overlapping illuminated fields or subfields, in the scan zone, especially in the near field, arising from too much intensity of the return illumination light, as well as dim areas, as a result of less or no overlap of the illuminated fields or subfields, in the scan zone, especially in the far field, arising from too little intensity of the return illumination light. Each such bright area could tend to blind or saturate the imager, and each such dim area could tend to cause imaging performance of the imager to be less responsive and sluggish, or even fail.
To counter the deleterious effects of bright light in the near field and dim light in the far field, and to help insure good imaging performance, it was known to properly expose each imager. Each imager was provided with an internal auto-exposure circuit for measuring the intensity level of the return illumination light in the field of view of the imager, and for responsively adjusting the exposure duration of the imager. As advantageous as such an internal auto-exposure circuit was, it only adjusted the exposure duration of the imager in which it was internally integrated, typically only after a few frames had elapsed. This non-negligible time delay created a sluggishly performing workstation and was, in some cases, perceived as defective.
Also, the single auto-exposure circuit internal to the single imager could only adjust the exposure duration uniformly for all the image sensors of the imager. Thus, in the case where split subfields were generated from one imager, it was further known to employ dedicated exposure sensors, one for each subfield. This, however, increased system complexity and overall cost of manufacture and assembly.
Accordingly, it would be desirable to uniformly illuminate fields of view in a point-of-transaction workstation and, more particularly, to uniformly illuminate subfields of view split from an imager in the workstation and, still more particularly, to provide sufficient and uniform illumination both in the near and the far fields of the workstation to achieve a wide dynamic range of working distances in which indicia may be successfully and rapidly imaged and read.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.